Call Routing Preference

[Rohit Khajuria]

HI All

I have a query related to Call Routing .

PFA the diagram for your reference.

Lets assume I have some sites connected to Call Manager in a distributed scenario. There are two routes for connectivity between the sites and Call Manager :

1. IPSec

2. MPLS

Now, as far as my understanding is concerned, if we are using IPSec the call will flow through call manager from one site to another site and If we are using MPLS, the sites will have direct connectivity and call doesnt have to flow via Call Manager.

And in the diagram, like I said we have both type of connectivities and we have defined preferences between the routes, means MPLS is given preference over IPSec. So accordingly, call will choose MPLS first in case of MPLS unavailablity it will choose IPSec and the call will flow via Call Manager.

We have dialpeers for both type of connectivities...means direct dialpeer to sotes and dialpeer towards call manager.

Now here comes my actual concern. What if I want to route the calls through IPSec first and then MPLS. And what I understand is we can change the preference, means we can give IPSec  preference over MPLS.

Or is it possible if I define preference in the dialpeers ... like dialpeers towards CM will have high preference and all other sites will have lower preference. This is my only doubt as dialpeers preference will not work if we have route preference defined.

Please comment and suggest.

Thanks all !!!

[pmvillarama]

CUCM or phones doesnt know ipsec or MPLS. but you need to make sure their traffic can reach its destination. you requirement depends on your routing table and i think you can use QoS to route signaling and media wherever you want them to.

[Rohit Khajuria]

I didnot get you. How QoS can be used to route traffic. As far as I know QoS is used for setting the preferences too and for quality purposes.

How QoS can come into the above scenario ? Could you please explain that ? May be I am missing something.

Thanks

[Vivek Batra]

What do you mean by call will or will not flow through CUCM?

Each call has two parts viz signlaing and media. Signaling will always pass through CUCM and media will always flow directly between the devices (avoiding MTP, Transcoding cases etc).

So CUCM responsibility is to connect media between two devices. What will be the route for media in the network won't be decided by CUCM. That is your network which decided the path. 

- Vivek

[Rohit Khajuria]

Hi Vivek

May be I am wrong but I think you didnt read the query carefully. I am talking of the distributed scenario not centralised scenario. So why would CUCM comes into the picture if we are dealing with distributed scenario ?

Ans yes you are absloutely rightthat each call has two parts i.e. signalling and media (RTP). and I am talking of signalling here as I know RTP flows between the endpoints .

Please correct me if I am wrong somewhere.

[Vivek Batra]

Before to make further comments, I would like to ask do you have one or two clusters? From the figure attached, I can see that there is only one CUCM cluster and all other sites have either CME or gateways. Isn't it?

- Vivek

[Rohit Khajuria]

Hi Vivek

I am talking of only one cluster now but in here we have mix environment. Some sites are centrally deployed and some are distributed deployed.

But at the moment I am only talking of the distributed deployed sites.

PFA another diagram for your reference . Sites A & B are centrally deployed wheras all other sites are distributed deployed.

[Vivek Batra]

I've bit difficulty in understnading the terms being used with reference to your question. I just comment here on the basis of my assumptions and you can correct me wherever required.

I further assume that all phones in different sites are registered with centralized CUCM cluster and not with CME.

So with respect to current question, we  have only one CUCM cluster, this means that we are referring to centralized call processing (intra-cluster) instead of distributed call processing (inter-cluster).

Since you've only one cluster, signaling will always pass through the phones respective call manager.

Now let say CUCM PUB IP address is 192.168.10.10 and SUB is 192.168.10.20, preference command in dial-peers will only decide whether first call attempt should be made to PUB or SUB depends on priority configured. Priority command in my opinion can't decide which network link should be used. If you're first attempting to send the call to SUB on 192.168.10.20, that's the routing table decided whether to use MPLS or IPSec or some other route to send the packets to that IP address.

Further you will use dial-peer mostly while making/recieving call to/from PSTN. However if there is IP Phone to IP Phone call, depends on the CMGroup assigned, phone will try to get registered first with respective CM node say again 192.168.15.20 so all singlaing from phone will go to that IP and network routing path will decide whetehr MPLS or IPSec should be used to transport those packets.

I'm not sure if my comments make sense to you but that is what I go from your last comment.

- Vivek 

[Rohit Khajuria]

Not at all, if the phones are registered with CUCM it would be centralised deployment.

If you had a look at the diagram only sites A & B have their phones registered with Call Manager, means these two sites are centrally deployed . But If I talk about the sites other than A & B , all the phones are registered locally (CME) means they are following distributed kind of deployment.

And my concern is only about the sites having distributed kind of deployment.

[Vivek Batra]

Thanks Rohit to clarify the installation scenerio. You're right. Since there are multiple call agents in your network, this should be visualized as distibuted network.

- Vivek

[Rohit Khajuria]

Always welcome Vivek !!!

[Ayodeji Okanlawon]

Rohit,

You can use dial-peer prefences to force calls to go via certain routes. So if you want your VOIP packets to go via IPSEC first and then MPLS as backup, then you can simple use dial-peer preferences to achieve this.

The path with the lowest preference is preferred first.

example below, IPSEC will be used first and MPLS as backup

dial-p v 1 v

destination-p 54..

session targ ipv4:10.10.10.10 ----IPSEC

pref 1

dtmf-re h245-alp

no vad

dial-p v 2 v

destination-p 54..

session targ ipv4:10.20.20.20 ----MPLS

pref 2

dtmf-re h245-alph

no vad

[Rohit Khajuria]

Thanks Ayodeji for your reply !! SO what I can understand from your reply is that there are two ways to achieve our goal. Either we can change IPSec and MPLS Preference or we can also change the dialpeer preference.

IPSec and MPLS Preference has nothing to do with call routing in that case.

[Ayodeji Okanlawon]

Rohit,

Yes, but they are two different things.

1. The first scenario where your gateway uses preferences to route the call

2. The second does have something to do with call routing, but the VOIP elements are not aware of it. Ultimately VOIP packets needs a means of transportation and whatever ip routes are available, is what will be used.

Calls will be routed based on whatever IP path you have provisioned. Using preferences forces the gateway to choose a certain path. Using IPSec and MPLS Preference will also ensure the traffic goes via the path you have chosen but this time, that path is transparent to the gateway.

[Rohit Khajuria]

Ok...SO in layman language I can say that Dailpeer will have preference over IPSec/MPLS for call routing in this type of scenario.